Illuminated and edge-lighted articles and methods of making same



Dec. 4, 1956 R. c. WEBSTER ILLUMINA'IED mu EDGE-LIGHTED ARTICLES AND METHODS OF MAKING SAME Filed Feb. 13, 1950 POROUS SHEET POROUS SHEET BEARING DECORATIVE OR ADVERTISING MATERIA m m w m United States Patent ILLUMINATED AND EDGE-LIGHTED ARTICLES AND METHODS OF MAKING SAME This invention relates to illuminated and edge-lighted articles; and, more particularly to composite illuminated and edge-lighted articles, and to methods of producing such articles.

It has been common practice in the display art to employ edge-lighted structures wherein lettering or designs or other advertising copy has been cut, or etched, or impressed by heated dies, into the rear surface of a plate of glass or transparent synthetic resinous material so that light projected into an edge of the plate is reflected or dispersed, upon contact with the lettering or copy, through the forward surface of the plate, and the lettering or copy thus illuminated. This method is subject to limitation of the advertising copy to relatively simple lettering or designs, with definite limitations on the ability to achieve fine details or gradations of color and value.

Past attempts to print the advertising or other copy directly on the surfaces of the light-carrying plastic or glass have required special apparatus for the printing; and, furthermore, detail as fine as that which can be obtained by printing on paper cannot be achieved by such methods, particularly with colored copy. My methods allow all this detail to be obtained, for the surface or print or copy to be displayed may first be printed on paper, and then the paper attached or bonded to the light-carrying medium in any one of several ways so that the surface can be beautifully illuminated. In addition, the surface to be displayed is well protected. If necessary, employing certain of my methods, paintings and irregular objects can be displayed and protected.

Previous attempts to edge-light advertising or other copy printed on paper attached to the rear surface of the light-carrying plastic or glass plate have failed, for a variety of reasons, to produce a commercially satisfactory article. Where the copy is attached by the use of adhesives, it often heretofore has been found difiicult or impossible to obtain a complete and secure bond; resulting in opaque areas and loss of illumination at all points of separation of the copy from the plate. Moreover, in composite articles so made, the illumination of the copy has been inadequate, either because the light projected into the plate does not sufficiently penetrate beyond the smooth rear surface of the plate or through the layer of air or the film of adhesivebetween the rear surface and the copy, or because, following the withdrawal of pressure heretofore exerted in connection with the application of the copy by the use of adhesives, innumerable very small voids are formed within the surface of the copy or between the plate and the copy, resulting in inadequate illumination and an overall graying or fogging of the copy. Attempts to apply printed or painted paper by impressing it into the rear surface of the plate while the surface is softened by heat, or by using a solvent of the plastic as an adhesive, have failed to produce articles capable of satisfactory edge-lighting because of the use of substantial pressure in the course of the application. In either case, upon the withdrawal of pressure, innumerable fine 2,772,997 Patented Dec. 4, 1956 ice 2 voids orbubbles have been formed, as above described, producing an unsatisfactory result. I p

Other methods of preparing structures of this general type have been developed employing specially prepared transfer sheets bearing advertising material which may be transferred by offset or other processes to one face of the transparent member. The articles thus produced have been found to be unsatisfactory in several respects. Either fine detail has been unobtainable or bubbles or voids have been present or the transfer sheets have required expensive elaborate equipment for their preparation, or the adhesives used have been unsatisfactory themselves because of any of several reasons.

The primary object of this invention is to provide a composite article consisting of a transparent fronting and an interstitial backing carrying printed or painted material and completely and optically bonded to therear surface of the plate or bedded therein without any deleterious distortion of any parts of the surface of the printing or painting or of the paper or other material on which the printing or painting occurs and essentially without voids of any sort in the surface of the printed or painted material or between it and the plate, so constitutedas to enable illumination of the printed or painted material, when viewed through the forward surface of the plate, by light projected into the plate at one or more of its edges.

Another object of this invention is to provide novel methods whereby printed or painted material carried by an interstitial backing may be completely and optically bonded to or bedded in the rear surface of a transparent fronting without deleterious distortion, in the process of application, of any partsof the surface of the printing or painting or of the paper or other material on which the printing or painting occurs and essentially without voids in the surface of the printing or painting or between it and the rear surface of the plate.

' The foregoing and other objects of this invention will be apparent from the following detailed descriptions and accompanying drawings. Inasmuch as the composite products, each of which falls within this invention, vary slightly from one another according to the method of fabrication employed, the description and drawings will be presented according to the particular methods of fabrication.

In the accompanying drawings:

Figure l is a side elevational view of an edge-lighted sign employing an illuminated composite article comprising this invention;

Figure 2 is an enlarged fragmentary sectional view of the illuminated composite article taken on line 22 of Figure l;

Figure 3 is a perspective view of an apparatus employed in forming the illuminated composite article shown in Figures 1 and 2; and

Figure 4 is a schematic view of a portion of the apparatus shown in Figure 3 illustrating one method of formi ng the illuminated composite article.

Method N0. 1

Referring to the drawings in detail, a form of edgelighted advertising display device is shown in Figure 1 which includes a support 1 having a lamp 2 disposed therein and an edge-lighted display panel 3 carried by the support. The display panel 3 embodying the invention consists of a composite or laminated illuminated article comprising a self-sustaining plate member 4 formed from a transparent synthetic resinous material which possesses the optical property of internally reflecting light rays when edge-lighted, a sheet 5 formed of a material having a porous or interstitial structure and having lettering, designs, pictorial representations, or other decorative material 6 applied thereto. Sheet 5 is integrally or unitarily bonded to the transparent plate 3 with the decorative material embedded in the rear surface of the synthetic resinous plate 4 (see Figure 2 for enlarged view of this). The transparent plate 4 may be formed of any synthetic resinous material which exhibits the phenomenon of internally reflecting light rays emanating from a light source disposed at one or more edges of the plate. This description will apply particularly to the Well known polymers of substituted or unsubstituted esters of acrylic acid; such as, for example, polymers of ethyl or methyl methacrylate, since such resins transmit internally reflected light rays with great efiiciency. However, the method can be used with other synthetic resinous materials possessing similar optical properties. The plate member 4 is of substantial thicie ness and self-sustaining to provide a rigid member which may be handledrwith facility during the operations employed in forming the composite article. This member must be clear, transparent and as free of defects as possible, since blemishes, distortions, scratches, air bubbles, or the like located either on the surface or within the body of the resinous material interrupt the transmission of the light projected into the plate, and become prominently illuminated and thus produce defects in the finished composite article.

The sheet 5 which bears the decorative material .6 may be formed of any substance which has a porous or interstitial structure, particularly, in the area thereof to be embedded in the synthetic resinous member and penetrated by the resinous material of said member, as will be described. It is preferred to employ a sheet of fibrous material; such as, for example, paper or a woven textile formed of either natural or synthetic fibers. If the sheet 5 is formed of paper, it is preferred to employ an unglazed or untreated stock, though sized or oil paper stock may be employed provided the porosity thereof is not destroyed and the surface thereby rendered incapable of being firmly bonded to the synthetic resinous material of which the transparent member 4 is formed by the penetration of the resinous material therefrom as hereinafter described. The sheet 5 may be a textile; and, while it is preferred to employ a closely woven cotton or rayon or othersynthetic fiber textile, roughly woven textiles in which the strands are not closely set may be employed if certain precautions are taken in the steps of forming the composite article. It is also possible to employ lightweight, thin sheets or blocks of other porous materials in which an interstitial structure is present in the area thereof to be embedded in the synthetic resinous material. The decorative material 6 may be applied to the face of the sheet 5 by any known process; such as, for example, direct or off-set printing, silk screen process or the equivalent.

The composite display panel 3 embodying this invention is a substantially unitary structure in which the plate member 4 and the sheet 5 are completely united by a strong, integral bond, and there is complete or almost complete absence of any voids in the surface of the sheet 5 or between it and the rear surface of the plate 4, and substantially complete'absence of any distortion, due to pressure in application, of any parts of the surface of the sheet 5, or of the decorative material thereon. The presence of such voids would cause graying or fogging, and diminished illumination of the decorative material as above stated. Some of the synthetic resinous material of which the transparent plate 4 is formed diffuses or migrates during the operation of forming the composite article so as to penetrate and extend into and fill the pores or interstices in and between the fibers of the sheet 5 and surround all prominences and fill all depressions in the surface of the printing or painting, so that they fit precisely into corresponding depressions or prominences, respectively, in the rear surface of the plate 4. Upon evaporation of the solvent used in the assembly process described below, the synthetic resinous material which has been dispersed or migrated into and about the fibres of sheet 5 and the decorative printing or painting thereon regains its original condition, with the result that the surface of sheet 5 and the decorative printing or painting thereon have been securely bedded in plate 4, with the further result that the rear surface of plate 4, which before processing had been mirror smooth, has become irregular in precise reverse of the forward surface of the attached sheet 5 and its decorative material, with the final result that light projected into plate 4 from an edge thereof, instead of being internally refiected from a smooth rear surface, is now diffused and reflected so as to fully illuminate sheet 5 and its decorative material when viewed through the forward surface of plate 4. The penetration of the synthetic resinous material into the sheet 5, and its hardening there, and the bedding of sheet 5 in plate 4, also result in their becoming securely bonded together. The composite illuminated articles embodying this invention, when edgelighted, provide an illumination of sheet 5, viewed through the forward surface of plate 4, which is practically equivalent to the illumination which would result from a light source of equal intensity disposed forward of plate 4 and directly surface lighting the decorative material.

The novel composite illuminated articles of this invention having the characteristics described above may be formed by a novel process employing the apparatus shown in Figure 3. This apparatus consists of a drum 7 which is about 12 inches in diameter and has a surfaces. The drum is mounted in a support 9 and arranged for rotation about its axis which is horizontally disposed. The terminal portions of the axle of the drum are journalled in the supports 9 to provide for smooth and free rotation of thedrum with the application or" a minimum amount of pressure exerted tangentially to the surface 8. A solvent reservoir 10 having a delivery tube 11 or multiple delivery tubes provided with a plurality of outlets 12 and a rate-of-flow control valve 33 are disposed above the drum surface S. A catch-basin 1 is positioned beneath the drum 7 to receive the solvent flowing from the drum surface, and pump means may be employed to return excess solvent to the reservoir 10 through the line 12a shown schematically, if desired.

The operation of forming the composite article by the method now being described is carried out by, first, placing the decorated sheet 5, face up, upon the surface 8 of the drum 7 and rotating the drum until the leading edge of the sheet 5 is located at the point on the circular path defined by the surface of the drum which it is desired to employ as a point of contact betweent the sheet 5 and the plate member 4 of transparent synthetic resinous material. A free flowing solvent for the synthetic resinous material, capable of dissolving the resin at a rapid rate, is then allowed to flow from the reservoir 10 through the outlets 12 in. the supply tube 11 over the portion of the sheet 5 adjacent the leading edge thereof, which solvent immediately saturates the leading edge and causes it to adhere to the drum with suificient firmness to insure the proper relationship between sheet 5 and plate 4 during the further processing. The plate memher 4 is then. placed by the operator upon the guide rails v 16 and then brought into contact with the leading edge of the sheet 5. The guide rails are capable of adjustment in respect of the distance between them so as to fit the sides of plate 4 and maintain the sides of the plate 4 in a relationship to the axis of' the drum during the rotation of the drum as described below. The rails are also capable of adjustment in such a manner that the contact between the under surface of plate 4 and the upper surface of sheet 5 (which sheet may vary in thickness) is reduced to the minimum pressure necessary to cause rotation of thedrum in the further processing as described below. The transparency of the plate 4 permits the operator to obtain proper registry of the sheet 5 with respect to plate 4. The drum, with sheet upon it, andLPlate 4:are held in contact without rotation of the drum long enough for the formation of a puddle of solvent at and adjacent to the point of contact of the face'of the sheet 5 and the surface of the synthetic resinous plate 4 as shown in the schematic drawing in Figure 4, which deposit of solvent must be continuously maintained during the rotation of the drum as described below, It is essentialthat bubbles in the solvent be permitted to rise and be released into the atmosphereinstead of'becoming entrapped between the sheet 5 and the transparent memher 4. When the continuing deposit of solvent has been formed, the operator then moves the plate 4 slowly downwardly in a straight line controlled by the guide rails 16, maintaining contact on the sheet 5 resting onthe arcuate surface 8. As this movement is performed the drum 7 is slowly rotated while the continuing deposit of solvent 15 remains adjacent to the point of contactand the excess of solvent flows off into the basin 14. The actual steps of applying the sheet 5 to the transparent member 4 as described above arecarried out by the operator without the application of any pressure tending to compress these elements together and distort the fibers of'the sheet 5 or the decorative material thereon; The relationship between the sheet 5, upon thedrum, and the lower surface of the plate 4 is such by virtue of the construction of the guide rails 16 and their adjustment, as above described, as to make it impossible forthe operator to employ a degree of pressure beyond that which is suflicient only to cause the drum 7 to rotate, which degree of pressure might be termed contact pressure. .The application of any pressure in excess of this amount tends to distort the fibers of the decorative sheet 5 and the surface of the decorativematerial thereon, and cause the formation of microscopic voids'as above described when the pressure is released, thus producing a grayness or fogging of the decorative material or, sheets, resulting in inefiicient illumination in the finished article when the latter is edge-lighted.

, After the movement of the transparent member 4; over the point of contact on the drum surface has been completed, so that all of the sheet 5 is adhered to the plate 4, the composite article thus formed should be disposed vertically to permit any excess solvent on plate 5 to drain off, and for the solvent to evaporate and thesynthetic resinous material to harden. j

The essential purpose of the creation and maintenance of the continuing deposit of solvent abovedescribed is to saturate the sheet 5 and to dissolve some of the synthetic resinous material in contact with the solvent. The dissolved resinous material diffuses or migrates into the saturated sheet 5, and, upon its regaining its original condition upon evaporation of the solvent, there results a, continuous and homogeneous resinous plate into which the forward surface of sheet 5 and its decorative material have been securely embedded as though. by the etching into the rear surface of plate '4 of the exact reverse of. the forward surface of the sheet 5 and its decorative material. The purpose of limiting the pressure 'of plate.

4 upon the sheet 5 to that which is just sufiicient to accomplish the rotational movement of the drum is toiavoid any distortion of the pigmented surface of, or the fibers within, sheet 5, since in the event of distortion by greater pressure and the recovery of normal position upon the removal of the pressure, particularly at a time of hardening or increased viscosity of the dissolved synthetic resinous material, innumerable microscopic or very small voids would be formed resulting in graying'or fogging and inadequate illumination of the sheet 5 when edgelighted.

The formation and proper maintenance of the continuing deposit of solvent depends to a minor extent upon the properties of the solvent employed; such as, for example, its viscosity,but primarily it depends upon the selectionof the point of contact on the surface of the drum 7 of the transparent member 4. It has been determined that the most desirable point of contact on the drum surface is that which provides an angle of from about 30-45 between a radial line of the drum passing through the point of contact and a horizontal radial line. It is preferred to employ a point of contact providing an angle of about 40 between the radial line extending through the point of contact and the horizontal. It will be apparent that the point of contact is subject to some variation depending upon other factors such as the viscosity of the solvent employed, the degree of porosity of the sheet 5 and the time necessary to permit escape of any bubbles in the solvent. What is essential is that the deposit of solvent be maintained long enough to permit the saturation of the adjacent portion of sheet 5 and the dissolving of resinous material in the adjacent surface of the plate 4. The guide rail' 16 is adjustable so as to vary the point of contact on the arcuate surface of the drum 7.

The choice of solvent in carrying out theabove process depends upon the type of synthetic resinous material employed in the transparent member 4. The properties which must he possessed by any solvent are free flowability or low viscosity and ability to dissolve the synthetic resinous material rapidly. If the transparent member 4 is formed of polymeric ethyl or methyl methacrylate the most satisfactory solvent which has been found is vinyl trichloride. Ethylene or methylene dichloride or mixtures thereof may be employed but these solvents are not as satisfactory as vinyl trichloride.

Trichloroethane or vinyl trichloride is inexpensive, and evaporates quickly, so that the finished product can be handled quickly; its properties are such that minor adjustrnents can be made before the paper becomes permanently fixed; it is relatively safe from the standpoint of explosiveness and toxicity; the bond is water resistant and is not damaged by the usual heat from the light source; and, lastly, this solvent dissolves the surface of the plastic extremely quickly producing the liquid plastic solution needed for the formation and perfection ,of the bond as above described. The optical properties of the bond or embedment by the method are as perfect as can be obtained because no foreign material remains between the surface of the copy and the light-carrying medium.

Occasionally, the solvent causes materials in the ink used in certain printing processes to run. If this occurs to an objectionable degree, the copy bearing surface can be first coated or sized with a thin application of a colorless transparent substance having an index of refraction fairly close to that of the light carrying plate. This coating substance must be resistant to the solvent used to dissolve the plastic. Many such substances are available commercially and their choice depends on the plastic and the solvent used. Among'such substances are zein and cellulose derivatives; such as, for example, Cellosize (hydroxyethyl cellulose) and the like. Another answer to thisproblem is to have the copy printed with inks which are not affected by the solvent used in this process. To avoid marring the surface of the plastic outside the area of attachment of the paper by solvent deposited thereon in the process of rolling the materials together on the drum, the paper may be placed on a-curved surface exactly the size of the paper, or very slightly smaller, this curved surface being elevated from the surface of the drum and traveling parallel to the surface of the drum.

This method has been described in detail using as materials, paper, ethyl or methyl methacrylate, and trichloroethane. However, the same method may be used employing many other materials to produce composite articles which lend themselves to display by edge-lighting techniques and which protect the surfaces to be displayed. Under certain conditions it may bedesirable to use a mixture which is more viscous than that which is produced by the use ofsolvent alone, as, for example, in attaching coarse or loose fabrics or. other very porous materials. Insuc'h instances, if the solvent alone'is used, not enough plastic -resin is dissolved to fill all the irregularities and interstices of the material to be attached using a mixture of the solvent and of the plastic in place of the solvent alone. The proportions of solvent and of plastic resin in' such solutions vary, depending upon the degree of irregularity or porosity of the surface to be attached. For most purposes the solution should be less than saturated. Such solutions can easily be made by mixing the desired proportions by weight of the solvent and the powdered iplastic resin or with larger pieces of the plastic resin. Appropriate enlargements or the outlets 12 in the supply pipe 11 may be necessary in view of increased viscosity; and, if the mixture is too viscous to flow through the orifices, it can be applied to the forward surface of the material to be attached by a brush or spray. With these minor variations or adjustments the process above described may be employed.

Instead of using fluorescent or incandescent light sources at the edge, ultraviolet light sources such as germicidal lamp tubes, can be used at the edge of the plastic. Lucite or Plexiglas transmit much of the ultraviolet spectrum extraordinarily well. Fluorescent and/ or phosphorescent dyes, paints, pigments, particles, etc., can be attached directly to the plastic by the methods described before in this application or by methods to be described later. These materials can be incorporated in inks and printed on paper or other materials and then attached using my processes if desired.

The composite illuminated articles embodying this invention and prepared by the process just described provide display panels of exceptionally attractive presentations of pictorial material which, when edge-lighted, are highly and efliciently illuminated. In addition to use in the field of advertising, an application of the illuminated composite articles of this invention is in the display of fine arts. Thus, prints of high quality may be employed as the decorative sheet 5. Such composite articles may be placed in a frame having a light source disposed adjacent one or more of the edges of the composite article. A print reproduction of a painting may be exhibited to excellent advantage.

Method N0. 2

due to the presence of adhesive between plate 4 and sheet 5. in Method No. 2 plate 4 maybe of glass, which was excluded from use in Method No. 1 because solvents for glass woulddamage the surface of sheet 5.

Previous attempts to edge-light advertising or other copy printed on paper attached to a light-carrying glass or plastic plate by adhesives have failed partly from the use of pressure in the application, resulting in the creation of voids or bubbles and fogging and inadequate illumination of the copy, as stated above, and partly from functional defects or inadequacies of the adhesives used.

In order to obtain satisfactory results, the adhesive must be one which is and will remain transparent and essentially colorless in the thickness used; which provides and maintains a complete and secure attachment; which does not yellow or become opaque or brittle or cracked or loosened with age or handling or from the heat from.

the light source; which allows of easy and inexpensive fabrication by the use of the apparatus and techniques described in Method No. 1; and, most importantly, must have an index of refraction the sameor substantiallythe same asth'a't ofthe material of which plate 4 is made. Only when all-thesc conditions exist can a bond be obtained'which is both mechanically and optically satisfactor-y, and a display panel created which edge-lights satisfactorily.

If the indices of refraction of the material of plate 4 and the adhesiveare the same or approximately the same, the plate and the adhesive are optically homogeneous and, in combination, are functionally the same as in case of display panelsmade by Method No. 1 where the material of the plate is continuous to the surface of sheet '5. If the indices of refraction of plate 4 and the adhesive are difierent, a substantial portion of the light rays impinging on the smooth rear surface of the plate will not pass beyond it, and the illumination of the surface of sheet 5 will be correspondingly and unsatisfactorily diminished.

The importance of optical homogeneity of plate 4 and the material between it and sheet 5 may be illustrated as follows:

If apiece of printed paper is held against the rear surface'of a plate ofglass or methyl or ethyl methacrylate, and light projected into an edge of the plate, there will be scarcely any illumination of the printed material, for the reason that the wide difierence in the indices of refraction 'of'the plate and of the air which lies between the plate and the sheet prevents passage of any more than a negligible portion of the light beyond the rear surface of the plate. If, then, the sheet is adhered to the plate by wetting it, the degree of illumination of the printing will be increased because the index of refraction of water is more close to that of the plate; but will still be unsatisfactory; As the water evaporates, small voids will appear 7 betweenthe plate and the sheet, resulting in fogging of the printing'and finally in complete loss of illumination as the separation of the sheet from the paper becomes complete.

If the adhesive is not transparent and colorless originally, or if it ceases to be so for any reason, its presence between the plate and the sheet impedes the transmission of light to the sheet or changes color values in an undesirable manner. If the adhesive becomes cracked with age-or handling or from'the heat of the light source or other cause, the cracks Will become illuminated and appearv as blemishes on the printed material of the sheet. If attachment of the sheet to the plate is lost for any cause, the resulting voids between the plate and the sheet, and the loss of continuity of the light carrying media, cause loss of illumination of the sheet ranging from fogging or graying of the surface of the sheet to complete loss of illumination according to the degree of separation. If more than contact pressure is employed in uniting the sheet and the plate with the adhesive, particularly where the adhesive contains volatile solvents, there results a distortion of the fibers or pigmentation of the surface of the sheet, and, uponwithdrawal of the pressure, the fibers and surface tend to regain their original position, causing the creationof voids which result in fogging or graying of the pictorialmaterial. Heat added to pressure under con ditions where a volatile solvent is present in the adhesive has uniformly produced even more unsatisfactory results. 7 Ishall mentionglass and methacrylate resins in particular indescribing Method No. 2, because these two materials .are the best which are commercially available at present in sheet form. With glass, first quality plate glass is preferred, commonly specified as mirror quality, highly polished, water white, and crystal clear. Plates of synthetic resin must be clear, transparent and as free from defects as possible eitherupon the surface or within the resinous material.

Only a few of the adhesives tested in developing Method No. 2 will be mentioned here. Any adhesive meeting therequirements mentioned above may beused. However, the method ofcuring? the adhesive depends on the adhesive itself.. Some require temperature higher. than.;room qtemperature-zto. effect setting or 1 vulcanizing;

Certain of them, while meeting all the requirements stated above, have the added virtue of remaining sufficiently soft for aperiod of a week or more as to enable the ready stripping of the sheet fromthe plate, and may therefore be used where it is desired to remove advertising copy after a limited period of use: and replace itwith other copy without the necessity of reprocessing the rear surface of the plate. Certain adhesives which have been found to be especially satisfactory are as follows;

Cuma'rWl, an adhesive manufacturedby The Barrett Company, Division of Allied Chemical and DyevCorporation. This is a coumarone-indeneresin manufactured from coal, tar, and naphtha. This cumar resin dissolved in benzol or other safer'organic solvents can be used, for example, to attach paper to'glass orimethacrylate, employing the techniques of Method No. 1 with the drum.

' L260, a polyvinyl acetate solvent solution, and

L-224, a polystyrene solvent solution, both manufactured by Bingham Brothers, Newark, New Jersey, can be used in the same way but precautions must be taken to insure that the glue line is very thin to avoid bubble formation.

MR26-C and MR29-C when used with catalysts, for example, benzoyl peroxide or Uniperox 60, can be employed in the same fashion. MR26-C and MR29-C are thermosetting casting resins of the polyester type. However, the cure requires much more time than does the solvent process using the trichloroethylene. They are manufactured by the Marco Chemical Company.

Cement #311-310 manufactured by the American Resinous Corporation is a vinyl adhesive and can be used with precautions taken to insure a thin glue line.

The cements, as furnished by the manufacturers, ordinarily are thicker or more viscous than would be ideal for our purposes. They, therefore, require in many cases thinning with appropriate solvents.

Some of the adhesives, otherwise satisfactory, tend to make ink on advertising copy run. This can be avoided by sizing'or coating the copy first with, for example, Cellosize or zein.

Cement Melurac 401 with catalysts can be used in this fashion to give good adherency on both glass and methacrylates. This Melurac 401 is a resin adhesive of the melamine-urea-formaldehyde group.

10 PVAL, manufactured by Bingham Brothers, is a polyvinyl alcohol aqueous solution and can be used if the surface of the paper is first protected by a coating or film, as mentioned before. The technique of application is similar to that described in Method No. 1. This cement gives good adherency to both glass and methacryla'tes.

Tygobond 30 which is manufactured by Chamberlain Engineering Corporation may be used as an excellent bond on both glass and methacrylate sheets. This is an adhesive based on blends of synthetic rubber and resins.

Bostik 6014 manufactured by B B Chemical Company, Cambridge, Massachusetts, is perhaps the best cement of all for some purposes. It is an almost colorless cement of the synthetic base solvent cement type soluble in aromatic organic solvents, and bonds extremely well to polyethylene, paper, aluminum foil and a number of other materials. a

I claim:

1. A laminated edge lighted display element comprising in combination, a backing member having a decorated front face of interstitial structure, a relatively thick selfsustaining transparent fronting therefor having a transparent edge and the property of internally reflecting light rays projected into it through said transparent edge, said transparent fronting having a substantially uniform index of refraction throughout its depth and a planar front surface and an interstitial rear surface and being free of any visible light refracting bubbles and having its interstitial rear surface extending into and so fully complementally filling the interstices of the decorated face of said backing member that it appears to have a completely common interface therewith that-gives noevi dence of separationby gaseous voids when viewed throughv parent self-sustaining relatively thick fronting body having a planar front surface and having an interstitial rear surface substantially completely complementary to and filling the interstices in the decoratedyfront face of the backing sheet and bonded thereto throughout the area thereof and thus having a unitary interface therewith throughout said area, said fronting body having a translucent edge and a substantially uniform indexof refraction throughout its depth from its front face to its interface and having the property of internally reflecting between said front face and interface light rays projected into it through said translucent edge said fronting body being illuminated for use through its translucent edge; whereby, on viewing the decorated interstitial backing through said front face under illumination by the light rays supplied through said translucent edge, a brilliant illumination of said decorated backing is observed unobscured by any reflections of said light rays from any interfacial surface other than that common to said backing.

3. An edge illuminated display according to claim 2, in which said edge lighted fronting body having a planar front surface and an interstitial rear surface complementary to the interstitial front face of the backing sheet is a homogeneous body of plastic material throughout its depth from its planar front surface to the extremities of its interstitial rear surface.

4. In the forming of an edge-lighted display element comprising a flexible sheet having a fibrous interstitial decorated surface adhesively secured to a transparent plate like member of material having the property of internally reflecting light rays supplied through an edge of the member, a method of obtaining a display that does not exhibit any greyish or silvery haze at the zone of adhesion and which thus affords a brilliant unhazed front view of the surface decoration of the sheet when viewed through the member under conditions of edge illumination, which method consists in arranging the sheet decorated face up as a convex arc, arranging the plate like member at a downward inclination and in tangential contact with a linear edge of the arched sheet below the crest of its arc, maintaining a pressure of the plate like member against the line of tangential contact at less than that which would appreciably distort the fibers of the sheet, flowing over the arcuate surface of the sheet a bubble free liquid capable of wetting the sheet and producing an adhesive bond between the sheet and the plate like member equal in index of refraction to that of the body of the plate like member and forming a well of said liquid between the arched sheet and plate adjacent the line of tangency thereof, then simultaneously linearly moving the plate like member and peripherally rotating the arcuate sheet to bring them progressively into liquid submerged contact at the line of tangency thereof while maintaining the well of bubble free liquid thereat so that the undeformed fibrous surface of the sheet is impregnated and its interstices filled with liquid adhesive material to the exclusion of bubbles and gaseous voids,

and permitting the bond to set.

5. A method according to claim 4 in which the plate like member is arranged and moved through the line of tangency at a downward inclination of between 30 and 45 6. A method according to claim 4 in which the plate like member is composed of synthetic resinous material and in which the liquid is a solvent for such synthetic resinous material.

7. A method according to claim 4 in which the plate like member is composed of methacrylate polymer and 1 1 r invvhich the-liquid isselected from the group consisting 2,013,867 of 'tfic'hloroethane and vinyl trichloride which are {free "2,079,641

7 flovving -fib'er wetting solvents of lowviscosity and ranid 2120;813 solvents for the polymer. 21293929 '8. A rnethod according to claim 4 in Whichthe plate 5 2,159,095 like member is composed of glassand in which'the liquid 2,166,819 is a solution of a resinous adhesive having a 'coffecient 2,264,628 of refraction substantially the same as that of the glass. 2,275,290

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529,073 Hoskins Nov. 13, 1894 2,517,698 1,538,858 Lindsay May 19, 1 9 25 2,518,726 1,968,095. Poschel July 31, 1934 15 2,548,126

7 V *12 Sloan Sept. 10, 1935 Walsh May 11, 1937 Riotte June 14, 1938 Gurwick Sept. 13, 1938 Madam May 23, 1939 Miller July 18, 1939 ,Engen Dec. 2, 1941 Dreyer Mar. 3, 1942 Barnhart Aug. 3, 1943 Gaylor Jan. 2, 1945 Lindh Jan. 23, 1945 Axelrod Mar. 14, 1950 Muskat Aug. 8, 1950 Schlenker Aug. 15, 1950 "Sholkin Apr. 10, 1951 

4. IN THE FORMING OF AN EDGE-LIGHTED DISPLAY ELEMENT COMPRISING A FLEXIBLE SHEET HAVING A FIBROUS INTERSTITIAL DECORATED SURFACE ADHESIVELY SECURED TO A TRANSPARENT PLATE LIKE MEMBER OF MATERIAL HAVING THE PROPERTY OF INTERNALLY REFLECTING LIGHT RAYS SUPPLIED THROUGH AN EDGE OF THE MEMBER, A METHOD OF OBTAINING A DISPLAY THAT DOES NOT EXHIBIT ANY GREYISH OR SILVERY HAZE AT THE ZONE OF ADHESION AND WHICH THUS AFFORDS A BRILLIANT UNHAZED FRONT VIEW OF THE SURFACE DECORATION OF THE SHEET WHEN VIEWED THROUGH THE MEMBER UNDER CONDITIONS OF EDGE ILLUMINATION, WHICH METHOD CONSISTS IN ARRANGING THE SHET DECORATED FACE UP AS A CONVEX ARC, ARRANGING THE PLATE LIKE MEMBER AT A DOWNWARD INCLINATION AND IN TANGENTIAL CONTACT WITH A LINEAR EDGE OF THE ARCHED SHEET BELOW THE CREST OF ITS ARC, MAINTAINING A PRESSURE OF THE PLATE LIKE MEMBER AGAINST THE LINE OF TANGENTIAL CONTACT AT LESS THAN THAT WHICH WOULD APPRECIABLY DISTORT THE FIBERS OF THE SHEET, FLOWING OVER THE ARCUATE SURFACE OF THE SHEET A BUBBLE FREE LIQUID CAPABLE OF WETTING THE SHEET AND PRODUCING AN ADHESIVE BOND BETWEEN THE SHEET AND THE PLATE LIKE MEMBER EQUAL IN INDEX OF REFRACTION TO THAT OF THE BODY OF THE PLATE LIKE MEMBER AND FORMING A WELL OF SAID LIQUID BETWEEN THE ARCHED SHEET AND PLATE ADJACENT THE LINE OF TANGENCY THEREOF, THEN SIMULTANEOUSLY LINEARLY MOVING THE PLATE LIKE MEMBER AND PERIPHERALLY ROTATING THE ARCUATE SHEET TO BRING THEM PROGESSIVELY INTO LIQUID SUBMERGED CONTACT AT THE LINE OF TANGENCY THEREOF WHILE MAINTAINING THE WELL OF BUBBLE FREE LIQUID THEREAT SO THAT THE UNDERFORMED FIBROUS SURFACE OF THE SHEET IS IMPREGNATED AND ITS INTERSTICES FILLED WITH LIQUID ADHESIVE MATERIAL TO THE EXCLUSION OF BUBBLES AND GASEOUS VOIDS, AND PERMITTING THE BOND TO SET. 